Digital time delay relay utilizing logic elements

ABSTRACT

Solid-state digital time delay relay having a pair of complementary contacts one of which breaks or opens before the other makes or closes. The switching or transfer function utilizes a light emitting diode in conjunction with a photosensitive resistive element for each set of contacts.

CROSS-REFERENCE TO RELATED APPLICATIONS

Certain inventions related to those disclosed in the present applicationare disclosed and claimed in copending application Ser. No. 501,570filed concurrently by G. F. Bogel and L. J. Sienkiewicz.

BACKGROUND OF THE INVENTION

This invention relates generally to solid-state time delay relays andthe invention relates specifically to relays of this type utilizingphotosensitive resistors used in conjunction with light emitting diodesto cause contact status change.

It is known to utilize solid-state time delayed relay devices havingcomplementary contacts. It would be advantageous if a solid-state relaydevice utilizing solid-state contacts could be provided which have abreak before make function in the complementary contacts. That is thecontact which is to open, opens before the contact which is to closecloses.

SUMMARY OF THE INVENTION

In accordance with the present invention a solid-state relay is taughtcomprising control means for actuating a solid state contact means tochange state. There are pro- a pair of complementary solid-statecontacts, one of which is generally open and the other which isgenerally closed except when the control means actuates the solid statecontacts to change state in which case the contact which is closed opensbefore the contact which is open closes. This is accomplished byutilizing a light emitting diode in conjunction with a photosensitiveresistive means. The previously described control means provides asignal to cause the light emitting diode to provide light energy whichimpinges upon the photosensitive resistive means causing it to changeits resistive value significantly. This resistive means is connected inone embodiment of the invention in such a manner as to effect the gatedrive voltage and current of a thyristor, thus causing the thyristor toconduct or not conduct depending upon the status of the light emittingdiode and photo resistive element.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention reference may be had to thepreferred embodiments exemplary of the invention shown in theaccompanying drawings in which:

FIG. 1 shows a solid-state digital timer utilizing an electrochemicalbreak before make function;

FIG. 2 shows a solid-state digital timer utilizing a logic element breakbefore make contact function; and

FIG. 3 shows concurrent wave-shapes for actuating portions of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and FIG. 1 in particular, there is showna digital time delay relay 10. The digital time relay comprises a sourceof electrical power S which provides in a preferred embodiment of theinvention, 60hertz alternating electrical current to a logic powersupply element 12. Logic power supply element 12 provides in thepreferred embodiment of the invention, 12 volt DC power between line 14and line 16 for logic elements in a remaining portion of the digitaltime relay 10. Line 16 is a system common line or system return which isconveniently interconnected with various portions of the relay 10.System common line 16 is electrically connected to the logic supply 12.The logic supply 12 also supplies a signal to a clock shaper element 18.Preferably the latter signal is a 120 hertz full wave rectified signal.The shaper 18 provides a series of alternating digital zeros and oneswhich in the preferred embodiment of the invention, are 0 volts and 12volts, respectively. There are two complementary output lines providedfor the shaper 18. A signal CL is provided to a divider circuit 20. Theother or complementary output signal CL is provided to another portionof the previously described divider circuit 20. The divider circuit 20may comprise in a preferred embodiment of the invention, a seven stagebinary counter 21 which is interconnected with a binary decoder 23 whichin turn is interconnected with a binary latching circuit 24. There isalso a switch S2 which is provided for determining the timing range ofthe digital time delay relay 10.

There is provided a reset which is utilized to carry a master resetsignal R which signal is utilized by an inverter Ab to provide acomplementary master reset signal R. The complementary reset signal R isprovided to the previously described divider 20 for resetting thedivider 20. The output of the divider 20 is provided at line 26 and isutilized for indexing a programmable decade counter L. The programmabledecade counter L records what is generally known as the leastsignificant digit provided from the output of the binary counter 21. Thedecade counter L is interconnected with a similar decade counter M whichis utilized to count the most significant digit provided by the outputof the binary counter 21. The output of the binary counter 21consequently is utilized to index the decade counter L and the decadecounter M through the decade counter L. The decade counters L and M areresettable through the master reset signal R. A disabled signal which isutilized to store a predetermined count on the decade counters L and M,is provided at a line 28. The output lines from the previously describeddecade counters L and M are generally designated 30 and 32 respectively.Both of the latter outputs are provided to an output logic circuit 34,the output logic circuit 34 has a decoder 36 interconnected with anoutput latch 38, and exclusive OR gate Fb and an exclusive OR gate Fc.The exclusive OR gates Fb and Fc drive amplifiers or inverter circuitsAd and Ae respectively. The previously described output logic circuit 34provides as one output signal thereof the previously described disablesignal on line 28. The output from the inverter Ad is provided to anon-overlapping isolator circuit ISO1. The output from the previouslydescribed inverter Ae is provided to a non-overlapping isolator circuitISO2. The non-overlapping isolator circuit ISO1 is utilized to controlthe solid-state, normally opened relay NO whereas the non-overlappingisolator circuit ISO2 is utilized to control the solid-state normallyclosed relay NC.

A source of power s is interconnected by way of a pilot relay or controlrelay PR to a rectifying circuit 40. Rectifying circuit 40 isinterconnected by way of a dual function latching and isolating circuit42 to a control logic circuit 44. The control logic circuit 44 isutilized in cooperation with a switch S1 to provide sufficient actuatinginformation to the ON delay or an OFF delay function element for thepreviously described normally opened and normally closed contacts NO andNC respectively.

The output of the previously described circuit 44 provides thepreviously described master reset signal R. There is also provided amultiple state light blinking or flashing circuit 46 which is utilizedto provide an indication of the status of the normally opened andnormally closed contacts NO and NC respectively and the status of thetiming operation during a timing cycle.

Digital Time Delay Relay Circuitry

The previously described source S is interconnected with a full wavediode bridge rectifier B1. Connected in series with the input terminalsof the previously described rectifier B1 is a noise suppressing andvoltage dropping resistor R1; connected across the input terminals ofthe rectifier B1 is a noise suppressing capacitor C2. The bridge B1 isconnected at one output terminal thereof to the anode of a diode D5, thecathode of which is connected to one side of a capacitor C1 and to oneend of a resistive element R2. The other end of the resistive element R2is connected to the regulating end of a Zener diode D6. The anode of theZener diode D6 and the other side of the capacitive element C1 areconnected to the other output terminal of the diode bridge B1. Thelatter output terminal also represents the previously described systemcommon line or return line 16.

The clock shaper circuit 18 comprises a voltage divider of resistors R3and R4 connected across the output terminals of the previously describeddiode bridge B1. Connected between the system common line 16 and thejunction between the resistors R3 and R4, is the input of an inverterAa1. The output of the inverter Aa1 is connected to the input of asecond inverter Aa2. The output of the second inverter Aa2 is fed backto the input of the first inverter Aa1 through resistive element R5.Also connected to the output of the first inverter Aa1 is thecomplementary clock output signal CL. The output of the second inverterAa2 is connected to line CL which is known as the clock output line.Line CL is connected as an input to the terminal i of the seven stagebinary counter circuit 20. The binary counter 21 may comprise asolid-state digital thin film integrated circuit module which has thecapability of dividing by either 12 or 120 depending upon the setting ofthe switch S2. The 2³ output terminal through the 2⁶ output terminal ofthe seven stage binary counter 21 are connected as inputs to thepreviously described NAND gate Eb. Likewise, the 2³ output terminal andthe 2² output terminal of the binary counter 21 are connected as inputsto the NAND gate Hb. The respective outputs of the two NAND gates Eb andHb, which comprise the decoder 23, are connected to the terminals of theswitch S2, the wiper of which is connected to one input terminal of aNAND gate Ea. The pole or wiper of the switch S2 may be alternatelyconnected to the output of the NAND gate Hb if a divide by 12 functionis desirable or may be connected to the output of the NAND gate Eb if adivide by 120 function is desirable. Connected as another input to thepreviously described NAND gate Ea is the complementary master resetsignal R. Also connected as an input to the NAND gate Ea is the outputfrom a complementary NAND gate. The output of the NAND gate Ea isconnected to an input of the previously described NAND gate Hc andlikewise the complementary clock signal CL is connected to another inputof the NAND gate Hc. NAND gates Ea and Hc cooperate to form thepreviously described latch 24. The output of a NAND gate Ea is connectedto line 26 which provides a positive going reset signal for the binarycounter 21 at input terminal r thereof and an indexing signal for thedecade counter L at an input terminal i1 thereof. An indexing signalfrom the decade counter L at terminal C1 is provided along line 27 to anindexing terminal of the decade counter M.

Switches S3 and S4 are utilized to choose one of ten possible outputterminals on each of the decade counters L and M. The output signalstherefrom are provided respectively along the lines 30 and 32 to two ofthe three input terminals of a NAND gate Ga. The third input to the NANDgate Ga comes from the master complementary reset R. The gate Ga is partof the output logic element 34 and comprises a portion of the time outdecoder 36. The output of the NAND gate Ga is connected to one inputterminal of a NAND gate Gb, the other input terminal of the gate Gb isinterconnected with the output terminal of a similar NAND gate Gc. Theoutput of the gate Gb, which is generally designated the time outterminal TO, is interconnected with an input terminal of the previouslydescribed gate Gc. The two cooperating NAND gates Gb and Gc comprise theoutput latch 38. A disable signal on line 28 is interconnected with thetime out terminal TO of the NAND gate Gb. The output terminal of theNAND gate gc is known as the complementary time out terminal TO. Themaster complementary reset signal R is also connected as one input ofthe NAND gate Gc. The time out terminal TO of the NAND gate Gb isconnected to one input terminal to an exclusive OR gate Fb. Anotherinput terminal of the exclusive OR gate Fb is connected by way of a line50 to switch S1 which has two positions. The two positions are forprogramming ON delay or OFF delay. The complementary output terminal TOof the NAND gate Gc is connected as one input to another exclusive ORgate Fc. The other input terminal of exclusive OR gate Fc is alsoconnected with the line 50. The output of the exclusive OR gate Fb isconnected to an amplifier Ad. The output of the exclusive OR gate Fc isconnected to an amplifier Ae. The amplifier Ad is interconnected by wayof a resistor R10 to the cathode of a light emitting diode P the anodeof which is connected to the positive power supply line 14. The lightemitting diode P cooperates with a photoresistor 52 to form part of thenonoverlap isolating circuit ISO1.

A terminal X for the normally open relay NO is connected to one side toa resistive element R14, to one end of a thyristor Q1 and to one end ofa resistive element R12. The other end of resistive element R12 isconnected to one side of the previously described photoresistor 52.Connected to the latter side of the photoresistor 52 is one side of acapacitive element C5 which is interconnected at the other end thereofby way of a solid-state control element Q3 to the gate of the previouslydescribed thyristor Q1. The other side of the resistive element R14 isconnected to one side of a capacitive element C7. The other side of thecapacitive element C7, the other side of the thyristor Q1, the otherside of the capacitive element C5 and the other side of thephotosensitive resistor 52 are all interconnected to the Y terminal of anormally opened relay NO.

In a similar fashion, the output terminal of the inverter Ae isconnected through a resistive element R1 to the cathode of a lightemitting diode K the anode of which is connected to the positive supplyline 14. The light emitting diode K cooperates with a photosensitiveresistor 54 to form the non-overlapping isolator ISO2. The Z terminal ofthe normally closed relay NC is connected to the one side of a resistiveelement R15, to one side of a thyristor element Q2 and to one side of aresistive element R13. The other side of the resistive element R13 isconnected concurrently to one side of the previously describedphotoresistor 54, to one side of a capacitive element C6 and through asolid-state control element Q4 to the gate of the previously describedthyristor Q2. The other side of the resistive element R15 is connectedto one side of capacitive element C8. The other side of the capacitiveelement C8, the other side of the thyristor element Q2, the other sideof the capacitive element C6 and the other side of the photoresistor 54are interconnected to the common terminal W for the normally closedrelay NC.

A power supply s is interconnected by way of a pilot relay PR to aresistor R6. Connected across the resistor R6 is the input of a diodebridge B2. The output of the diode bridge B2 is connected at one sidethereof to the regulating terminal of the Zener diode D11 and at theother side thereof to a bridge common line 41. The other terminal of theZener diode Z11 is connected concurrently to one side of a resistiveelement R7 and to one side of a capacitive element C4. The other side ofthe capacitive element C4 is connected to line 41. The other side of theresistive element R7 is connected to the anode of a light emitting diodeB the other end of which is connected to line 41. The light emittingdiode B cooperates with a phototransistor QP to form a combinationlatching and isolating circuit 42. The emitter of transistor QP isconnected to the system common line 16. The base of the transistor QP isconnected to one side of a resistive element R9. The collector of thephototransistor QP is connected to one side of a resistive element R8and to the input of an inverter Ac. The other side of the resistiveelement R8 is connected to the power supply line 14. The output of theinverter Ac is connected to the other side of the resistive element R9for positive feedback for the phototransistor QD and is also connectedto one input terminal of an exclusive OR gate Fa. The other inputterminal of the exclusive OR gate Fa is connected to the pole of theswitch S1. The output of the exclusive OR gate Fa comprises the masterreset terminal R. The master reset line or terminal R is connected tothe input of an inverter Ab which provides at its output thecomplementary master reset signal R.

A light blinker circuit 46 is provided which comprises a NAND gate Hdone input terminal of which is connected to the previously describedcomplementary output terminal TO of the output latch 38 of the outputlogic circuit 34. The other input terminal of the NAND gate Hd isconnected to the 2³ output terminal of the previously described sevenstage binary counter 21. The output terminal of the NAND gate Hd isconnected to one input terminal of an exclusive OR gate Fd. Anotherinput terminal of the exclusive OR gate Fd is connected to the outputterminal of the exclusive OR gate Fb. The output terminal of theexclusive OR gate Fd is connected to the input terminal of an amplifieror inverter Af. The output terminal of the amplifier or inverter Af isconnected by way of a serially connected resistor R16 to the cathode ofa light emitting diode D12, the other side of which is connected to thepositive power supply line 14.

The switch S1 has the ON delay stationary terminal thereof connected tothe positive power supply line 14 and the OFF delay stationary terminalthereof connected to the system common line 16. The pole of the switchS1 is movable between the latter two terminals.

Operation of the Digital Time Delay Relay

The source S in a preferred embodiment of the invention provides 60hertz alternating current to the bridge B1. The resistive element R1 isutilized for voltage drop and noise suppression. Capacitive element C2is also used as part of the noise suppression network. The capacitiveelement C1 cooperates with the resistive element R2 and the Zener diodeD6 to provide a DC power supply voltage for the elements of the timedelay circuit 10 between lines 14 and 16. In a preferred embodiment ofthe invention the DC power supply voltage is 12 volts, positive. Thediode D5 cooperates with the bridge B1 and the capacitive element C1 toclip the 120 hertz full wave rectified signal coming from the outputterminals of the diode bridge B1. The voltage divider network comprisingresistive elements R3 and R4 cooperates with the last named element tofurther reduce the voltage which is supplied to the inverter Aa1. Theoutput signal from the inverter Aa 1 is provided to another inverterAa2. The clock shaper 18 which comprises the inverters Aa1 and Aa2performs a waveshaping function, that is it provides at the outputterminals thereof proper pulses in terms of both waveshape and amplitudewhich may be utilized in the logic circuitry of the digital time delayrelay 10.

Certain portions or elements of the digital time delay relay circuit 10perform necessary functions which will be discussed at this time.

The inverters such as Aa1, Aa2, etc. invert the input signals providedthereto. As an example, if a binary one is placed on the input terminalthereof a binary zero will appear on the output terminal thereof. If abinary or digital zero is applied to the input terminal thereof, abinary or digital one will appear on the output terminal thereof.

The seven stage binary counter 21 has power supply terminals u and y forconnecting to the positive and negative power supply lines 14 and 16respectively. Counter 21 also has a reset terminal r where reset of thecounter 21 will occur on a positive going pulse, that is a pulse thatchanges from a binary zero to a binary one. Counter 21 has an input orindexing terminal i where a signal is provided for causing the variousbinary output terminals to cooperate to give a count from zero to 127.There are seven different output terminals which are generallydesignated 0 to 6 and which represent 2⁰ on the left to 2⁶ on the right.

The decade counters L and M have power supply and reset terminals (notidentified). The decade counters L and M also have an input or indexingterminal i1 and i2 respectively and a carry out terminal c1 whichprovides a signal after each decade has been counted on the decadecounter. There are also 10 decade output terminals ranging from 0through 9 one of which is at a binary one and nine of which are atbinary zeros at all times. There is a disabled or freeze terminal fwhich when energized, will freeze or maintain the present or existingdecimal output count even though signals continue to change at the inputterminal i1 or i2 as the case may be of the counter.

There are NAND gates such as Ga, Hb and Ea etc. which have thecharacteristic of providing a digital one at the output terminal thereofif there is a digital zero on any input terminal thereof but providing adigital zero on the output terminal thereof only if there is a digitalone on all input terminals thereof.

There are also the exclusive OR gates such as Fb, Fc, etc. which havethe function of providing a digital zero output if all the inputterminals thereof have the same digital signal thereof. That is, ifthere are two input terminals for the exclusive OR gate and both are atdigital one or both are at digital zero the output of the exclusive ORgate is a digital zero. However, if one or the other input terminal isat digital one and the remaining terminal is at a digital zero, theoutput terminal will be at digital one. This gives the exclusive OR gatethe characteristic of a programmable or controllable inverter. If one ofthe two input terminals is maintained at a digital zero then the signalon the other input terminal will be passed through the exclusive OR gatewithout inversion. However, if one of the input terminals is maintainedat a digital one, the signal on the other terminal will pass through theexclusive OR gate with inversion.

Illustrative Example

In order to aid in describing the operation of the digital time delayrelay 10, the description of the operation of the parts and elementsthereof will be described in the context of an illustrative example. Inthe illustrative example, it is desired to provide an OFF time delayfunction for the normally opened contact NO, where the OFF delay is 29seconds. To accomplish this switch S1 is placed in the OFF delayposition which interconnects the wiper of switch 1 to the system commonline 16 thereby placing a binary zero on the wiper of switch S1. Thewiper of switch S2 is connected to the output terminal of the Eb NANDgate. Switch S3, which is the least significant digit switch isconnected to the 9 output terminal of the decade counter L and switch S4which is the most significant digit switch is connnected to the 2terminal of the decade counter M. In this example, the closing of thepilot relay PR should be thought of as providing a signal to close thenormally opened contacts NO between the terminals X and Y. Thesubsequent opening of the pilot or control contact or relay PR willcause an opening of the now closed but normally opened contacts NO, 29seconds later.

Closing the switch PR interconnects the power supply s to the diodebridge B2. From the output terminals of the diode bridge B2 a full waverectified signal which in a preferred embodiment of the invention is 180volts peak is applied across the serial combination of the capacitiveelement C4 and the Zener diode D11. The junction terminal of theserially connected latter elements provides a regulated DC voltagethereat. This signal is applied to the series combination of theresistive element R7 and the light emitting diode B. The resistor R7 isa current limiting resistor. The current flowing through the diode Bprovides light which impinges upon the light sensitive base of thephotosensitive transistor QP, thus driving the photosensitive transistorQP, into saturation causing a digital zero to be placed on the inputterminal of the inverter Ac which in turn causes a digital one to beplaced on the output terminal thereof. The digital one on the outputterminal of the inverter Ac provides current through the resistiveelement R9 to the base lead of the transistor QP thus further drivingthe transistor QP into saturation for latching. Since a binary zeroexists on the control terminal of the two terminal exclusive OR gate Faa signal provided to the other terminal thereof will be fed therethroughwithout inversion. In this case, the previously described digital one onthe output terminal of the inverter Ac is also present on the outputterminal of the exclusive OR gate Fa. The positive going leading edge ofthis signal which is also known as the master reset signal R resets thetwo previously described decade counters L and M at the reset terminalsr1 and r2 thereof respectively. Consequently, the zero output terminalsof the decade counters L and M are both at a digital one and the othernine terminals are all at a digital zero. Since the switches S3 and S4are connected respectively to the 9 output terminal of the decadecounter L and 2 output terminal of the decade counter M, the first twoinput terminals for the time out decoder 36 NAND gate Ga are at binaryzero. The output terminals of the exclusive OR gate Fa is also connectedto the input terminal of the inverter Ab. The output terminal of theinverter Ab therefore has impressed thereon that any instant of time thecomplementary master reset signal generally known as R. This signal isprovided concurrently to three NAND gates, namely NAND gate Ga, NANDgate Gc and NAND gate Ea. When the master reset signal R is at a binaryone, the complementary reset signal R must be at a binary zero. Since abinary zero on any terminal of an NAND gate provides binary one at theoutput terminal thereof it can be seen that the output terminal of theNAND gate Gc is at one and the output terminal of a NAND gate Ga is atone. The output terminal of the NAND gate Gc is fed back to one inputterminal of the NAND gate Gb. The output terminal of a NAND gate Ga isfed to the other terminal of the NAND gate Gc. Consequently, two binaryones are present on the only two terminals of NAND gate Gb causing abinary zero to exist at the output terminal thereof. The output terminalof NAND gate Gb is fed back to the other input terminal of the NAND gateGc placing another zero on its remaining input terminal thus latching orholding the output terminal thereof in the binary 1 state. The exclusiveOR gate Fb has a binary zero on one control terminal thereof at line 50.Consequently, the binary zero on the other terminal thereof, that is,the output signal from the NAND gate Gb is passed through the exclusiveOR gate Fb without inversion, and is provided to the input terminal ofthe inverter Ad which places a binary one on the output terminalthereof. This removes the sink for current from line 14 through thelight emitting diode P and the current limiting resistor R10. Removingthis current causes the photoelectrical or photochemical resistiveelement 52 to relatively slowly change its resistance from approximately1K ohm to approximately 10 megohm in a preferred embodiment.Consequently, the voltage existing between the terminals X and Ycooperates with the resistive element R12 and the capacitive element C5as well as the solid-state device Q3, to energize the gate of thethyristor or similar gated element Q1. This has the effect of closingthe normally opened relay contacts NO and providing a current flowthrough the load LD and the source Su serially connected thereto. Theresistive element R4 and capacitive element C7 are seriallyinterconnected across the thyristor element for noise suppressionpurposes. Consequently, it can be seen that by closing the control relayPR the normally opened contacts NO are closed after a relatively shortreset time.

The binary zero which was supplied to one terminal of the NAND gate Eaguarantees that a binary one is placed on the output terminal thereof.This binary one is fed back to the one input terminal of a NAND gate Hc.The clock bar signal CL from the output terminal of the inverter Aa1 isprovided to the other input terminal of the NAND gate Hc, when itbecomes a digital one which occurs 120 times every second, the outputterminal thereof has a digital zero then placed thereacross which is fedback to an input terminal of the previously described NAND gate Ea,which generally guarantees that the latch combination 24 comprising theNAND gates Ea and Hc remain latched for the length of one clock pulse.The positive going pulse on the output terminal of the NAND gate Ea, asit changes from a binary zero to a binary one in concurrence with theclosing of the switch PR, resets the seven stage binary counter 21 atthe reset terminal r thereof. At this time the decade counters L and Mare in the reset state which insures that there is a digital or binaryone on the 0 decade terminal thereof. After reset has occurred, in theseven stage binary counter 21, the four input terminals connected to thedecoder NAND gate Eb all go to zero, causing a one to be present at theoutput terminal of the NAND gate Eb. This digital one is provided to oneof the input terminals of the NAND gate Ea through the switch S2. At arate of 120 hertz the clock bar pulse CL provided to one of the inputterminals of the NAND gate H c goes to one thus setting up anopportunity for the output terminal of the NAND gate Ea to go to one.However, this will not happen as long as one zero is present on oneinput terminal thereof and that will be the case as long as the relay PRis closed.

As was described previously, when the relay PR is opened, it is desiredto open the now-closed contacts NO between the terminals X and Y after a29 second delay. When the relay PR opens, the current through the diodeB decreases consequently causing the transistor QP to turn off. Thisplaces a binary zero at the output terminal of the inverter Ac whichprovides a sink for current from the base of the transistor QP throughthe resistor R9 which therfore latches the transistor QP off. The binaryzero is passed through the exclusive OR gate Fa and is inverted by theinverter Ab. Consequently, the complementary master reset signal Rchanges status from binary zero to binary one. This pplaces a binary oneon at least one input terminal each of the NAND gates Ea, Ga and Gc.Since some zeros exist on other input terminals of the NAND gates Ga andGc no change occurs at the output terminals thereof. However, it is mostlikely that a binary one is also present on the output terminal of thedecoder NAND gate Eb. This is because it is most likely that at leastone of the input terminals thereof has a zero thereon. On the nextoccurrence of the presence of a zero on the clock bar CL input terminalof the NAND gate Hc, its output terminal will go to one and consequentlya coincidence of ones on all of the input terminals of the NAND gate Eawill occur and the output terminal thereof will then go to zero. Thiswill start the 29 second countdown for the subsequent opening of thesolid-state relay contact NO between the terminals X and Y. This willnot have an effect on the decade counters L and M, as it takes apositive pulse to effect these functions. However, as soon as one zerois present, on any one of the input terminals of the NAND gate Ea, itwill change status at the output thereof from zero to one. This willoccur when the output terminal of the NAND gate Eb goes to zero whichwill occur after 1 second when all its input terminals are at one orwhen a count of 120 is registered on the binary output. Once everysecond, the output terminal of the NAND gate Eb will go to one, thuscausing reset of the binary counter 21 and indexing of the decadecounters L and M if appropriate.

After 29 seconds, the decade counters L and M will be in such a statethat all three of the inputs to the time out decoder NAND gate Ga willbe digital ones thus causing the output of that NAND gate Ga to go tozero, thus causing the output of the sequentially connected NAND gate Gbto go to one, thus causing the exclusive OR gate output to go to one,thus causing the output of the amplifier Ad to go to zero, to thus startthe current flowing in the light emitting diode P. This causes theresistance of the photoresistive control element 52 to rapidly changefrom approximately 10 megohms to approximately 1K ohm thus causing thethyristor element Q1 to cease to conduct, thus effectively opening therelay NO between the terminals X and Y.

While the above described operation occurred with respect to thenormally opened contacts NO, a similar and related operation wasoccurring with respect to the normally closed contacts NC. The originalenergization or depression or the relay PR caused a zero to be placed onthe output terminal of the inverter Ae thus causing a large amount ofcurrents to flow from the line 14 through the light emitting diode K andthe current limiting resistor R11. This caused the photoresistiveelement 54 to relatively rapidly have a very low resistance,approximately 1000 ohms, to thereby cooperate with the resistive elementR13, the capacitive element C6 and the control element or siliconebilateral switch Q4 to open the thyristor or triac Q2. Later when thenormally opened relay was once again opened after the 29 second delay,the normally closed relay once again closed by action of the relativelyslower increase resistance in the photoresistor 54. Thus, it is aproperty of the isolating and non-overlapping stages ISO1 and ISO2 tocause a break before making function for the two relays, NO and NC. Saidin another way, when a situation arises where the relays NO and NC areeach to change state theoretically generally simultaneously, that relaywhich is opening will always open a short period of time before theother relay closes.

The light emitting diode D12 is provided to give an indication of thestatus of the contacts NC and NO. In this embodiment of the invention,the light emitting diode will be illuminated or lit when the normallyopened contact is closed (normally closed contact NC opened). Diode D12will be dark or non-illuminating when the normally opened contact NO isopened (normally closed contact NC closed). The light emitting diode D12will blink during time out whether it be a time delay to close or a timedelay to open situation, and whether it be a divide by 12 or divide by120 situation. In the latter case the flash frequency will vary betweenthe divide by 12 and divide by 120 situation. Also the pattern ofblinking, though hardly noticable will be complementary or invertedbetween the time out to open and the time out to close situation. Thediode D12 will emit light when the output of inverter Af goes low toprovide a sink for current from line 14. The diode D12 will not emitlight when the output of the inverter Af goes high. The disposition ofthe output of the inverter Af is directly affected by the status of theoutput of the exclusive OR gate Fd. The status of the top input terminalof the exclusive OR gate Fd determines whether the exclusive OR gate Fdinverts the signal on the bottom terminal or not. The status of thebottom terminal is determined by the status of the output of the NANDgate Hd which in turn is dependent upon the status of its inputterminals. The status of the output terminal of NAND gate Hd is eitherhigh, low or oscillating at a frequency dependent mainly upon whether adivide by 12 or a divide by 120 function is being utilized. In a divideby 12 situation the blinking frequency of the light emitting diode isgenerally 8 to 4, that is it will be in one state for 8 counts or untilthe 2³ output 3 of the device 21 comes high and then will remain inanother state until reset by the counter 21 at the occurrence of thetwelfth clock pulse CL. The proceeding operation will occur at 10 hertzrate. In a divide by 120 situation the blinking frequency of the lightemitting diode is generally 8 to 8 with a timing mark occurring at the120th pulse. This provides a 7.5 hertz rate with a timing indicationevery second.

Second Illustrative Example

By way of a second illustrative example, the cooperation among theelements in the digital time delay relay 10 will be further explained.Presume it is desirous to change the states of the normally openedcontacts NO and the normally closed contacts NC such that there is an ONdelay of 0.9 seconds for the normally opened contact NO. In this case,the switch S1 will be thrown from the OFF delay position to the ON delayposition. Switch S3 will be maintained in the g position of the decadecounter L and switch S4 will be placed in the 0 position of the decadecounter M. Switch S2 will be switched from the output of the Eb NANDgate to the output of the Hb NAND gate. The exclusive OR gates Fb, Fcand Fa are thus converted from a non-inverting to an inverting state.The desired function in this case, is to have the normally opened relayclose and the normally closed relay open 0.9 seconds after the controlrelay PR is closed. It is important to remember with respect to thedigital time delay relay 10 that if the pilot control PR is open themere energizing of the power supply circuit 12 automatically causesreset of all the appropriate devices, automatically causes the normallyopened contact NO to open and automatically causes the normally closedcontact NC to close. Consequently, no action is required with the relayPR initially as was the case with respect to the off delay case. Oncethe relay PR is closed, the output of the exclusive OR gate Fa goes lowor goes to a digital zero, because the exclusive OR gate Fa is now in aninverting mode. Consequently, the complementary master reset signal R atthe output of the amplifier Ab goes to a one. This places a one on oneof the inputs of the NAND gate Ea. It is also likely that the output ofthe NAND gate Hd is also at one because it is impossible for the twoinputs provided thereto to be both at a one level at this time, counter21 having been reset. On the occurrence of the complementary clocksignal CL going to the zero state the NAND gate Hc will go to the onestate at the output thereof, thus providing digital ones on all theinputs of the NAND gate Ea thus providing a digital zero on the outputthereof. The input of the decoder NAND gate Hb is such that it willprovide a zero on the output thereof once every 1/10 of a second, thatis every 12 counts of the 120 hertz clock signal CL. The presence of thezero on the output of the NAND gate Hb will cause a subsequent reset ofthe counter 21 and an indexing of the decade counters L and M. When thedecade counter L has been indexed to the ninth position, a digital oneis provided at the wiper of the switch S3 which is fed to one inputterminal of the NAND gate Ga. Since the switch S4 is now connected tothe zero terminal of the counter M, the input terminal of the gate Gaconnected thereto is already at a binary one. Finally, the enabling orreset terminal of the gate Ga, which is the only remaining inputterminal therefor and which is connected to the output of the inverterAb is also already at a binary one. Consequently, the output of the gateGa will go to zero forcing the output of the gate Gb to go to one whichthus interacts with the NAND gate Gc causing its output to go to zero.The exclusive OR gate Fc will have output go to one because it is nowdisposed in the inverting state. This causes the output of the inverterAe to go to zero causing the current from the light emitting diode K togo high thus causing the resistance of the element 54 to go low. At thesame time the output of the exclusive OR gate Fb will go to zero,causing the output of the inverted Ad to go to one, causing theresistance of element 52 to go high. This causes the thyristor Q1 toconduct in a manner that was described previously, thus closing normallyopened contact NO. In this condition the light emitting diode 12 will beilluminated to indicate that the normally opened contact is now closed.In a like manner, the normally closed contact NC will be opened.

Referring now to FIG. 2, there is shown another embodiment of theinvention in which the break before make concept described previouslyutilizes logic control elements rather than electrochemical elements. Aclock shaper CS is provided which has its input connected to a switch S5the wiper of which may be movable between line LN or an independentoscillator OSC. In this case the switch S5 is shown connected to theline LN. The output of the clock shaper CS may comprise a 120 hertzclock signal c1 which is in the form of serial pulses. This signal maybe provided to an inverter I1 to provide a complementary clock signal c1at its output. The clock signal c1 is provided to a divide-by-12-counterD12. The counter D12 may comprise a divide-by-two-counter D2 connectedin series with a divide-by-6-counter D6. In this embodiment of theinvention the counter D6 has a separate "set" terminal SE and a separate"reset" terminal R1A. The output of the counter D2 may be provided to aseparate line 78 for utilization in other portions of the circuit D12.The output of the counter D12 may be provided to a divide-by-10-counterD10 the output of which is provided to a range selector switch RS.Alternately, the output of the counter D12 may be provided directly tothe range selector switch RS. The output of the counter D12 may also beprovided to a separate line 80 for utilization in other portions of thecircuit. The reset terminal R1A for the counter D12 is connected to areset line 82. In the same manner the reset R1B for the counter D10 isalso connected to the reset line 82. Depending upon the disposition ofthe range selector RS, the output of the counter D10 may be provided atthe output of the range selector switch RS or the output of the counterD12 may be provided at the output of the range selector switch RS. Theoutput signal of the counter D12 in the preferred embodiment of theinvention is a 10 hertz signal while the output of the counter D10 in apreferred embodiment of the invention is a 1 hertz signal. The output ofthe range selector switch RS is provided to the input of adecade-counter-for-units DCU. The counter DCU may be preset to a givenvalue from zero to nine at the preset control DCUS. The output 01 of thedecade counter DCU is provided to a decade-counter-for-tens functionalblock DCT. The output 02 of counter DCU is provided through an inverterI5 to one input of a NOR gate N1. A number may be preset at the presetcontrol DCTS in the counter DCT. The output of the functional block DCTis provided through an inverter I6 to another input terminal of thepreviously described NOR gate N1. The decade counter DCU and the decadecounter DCT also have present enable terminals R1C and R1D respectivelywhich are both connected to the previously described reset line 82. Thepreviously described complementary clock signal line c1 and thepreviously described line 78 are both connected as inputs to a NOR gateN8. The output of the NOR gate N8 is provided as an input to an AND gateA1. There is also provided an exclusive OR gate X01. The mode ofoperation of an exclusive OR gate was described previously with respectto FIG. 1. The output of the exclusive OR gate X01 is providedsimultaneously to the reset line 82 and to the remaining terminal of theNOR gate N1 and the AND gate A1. The output of the NOR gate N1 isprovided as one input to a NOR gate N2 the output of which is connectedas one input to a NOR gate N3. The other input of the NOR gate N3 isconnected to the output of the AND gate A1. The output of the NOR gateN3 is connected to the other input terminal of the NOR gate N2. Theoutput of the NOR gate N3 is also connected to the set terminal SE ofthe previously described divider D12 and to one input terminal of anexclusive OR gate X02. Both the set terminal SE and reset terminal R1Aof the counter D12 are connected internally to the counter D6 which isof course a portion of the counter D12. Consequently, thedivide-by-2-counter D2 portion of the divide-by-12-counter D12 is notcontrolled by the reset line 82 nor the set terminal SE.

There is provided a control functional block C having a switch means s1therein which is movable between an opened and closed position. In apreferred embodiment of the invention, the control C may be thought ofas the control which causes the normally closed and normally openedcontacts NC and NO to operate. In a preferred embodiment of theinvention the control C may be thought of as providing an energizingsignal when its output is a digital one and may be thought of asproviding a non-energizing signal when its output is a digital zero. Theswitch s1 is utilized to control the difference in output signals forthe control unit C. The output of the control unit C is provided to oneterminal of the previously described exclusive OR gate X01. There isalso provided an on/off delay selector D, the output of the on/off delayselector D is provided simultaneously to the remaining input terminal ofthe exclusive OR gate X01, to the remaining terminal of the exclusive ORgate X02 and to a terminal of an exclusive OR gate X03. Each of theseterminals are generally designated P indicating that they areprogrammable depending upon the disposition of the on/off delay controlD. Generally an on delay signal from the control unit D will provide adigital one at the previously described P terminal and an off delaysignal will provide a digital zero at the previously described terminalP. Connected to the remaining input terminal of the previously describedexclusive OR gate X03 is the line 80. The output of the exclusive ORgate X03 is connected to a light indicating means or light emittingdiode means LED. The output of the exclusive OR gate X02 is provided tothe input terminal of an inverter I2, to one input terminal of an ANDgate A2, and to one input terminal of a NOR gate N4. The output of theinverter I2 is provided simultaneously to one terminal of a NOR gate N5and to one input terminal of an AND gate A3. The remaining inputterminal of each of the AND gates A2 and A3 is connected to the line 78.These terminals are generally designated e as is one of the inputterminals for the NOR gate N8. The output terminal of the AND gate A2 isconnected to an input terminal of a NOR gate N6. The output terminal ofthe AND gate A3 is connected to the input terminal of a NOR gate N7. Theoutput terminal of the NOR gate N5 is connected to the remaining inputterminal of the NOR gate N6, and the output terminal of the NOR gate N6is connected to the remaining input terminal of the NOR gate N5. In alike manner, the output terminal of the NOR gate N4 is connected to theremaining input terminal of the NOR gate N7 and the output terminal ofthe NOR gate N7 is connected to the remaining input terminal of the NORgate N4. The output terminal of the NOR gate N6 is also connected to theinput terminal of an inverter I3, the output of which controls the gateg1 of a thyristor th1. The anode circuit NC of the thyristor th1 isconnected in series circuit relationship with a power supply PS1 and aload LD1. The output of the NOR gate N7 is connected to the inputterminal of an inverter I4 the output of which is connected to the gateg2 of a thyristor th2. The anode circuit NO of the thyristor th2 isconnected in series circuit relationship with power supply means PS2 anda load means LD2. The circuit including the thyristor th1 generally mustbe opened if the circuit containing the thyristor th2 is closed and viceversa.

OPERATION

By way of an illustrative example, presume that it is desired to have anON delay for the opening of the normally closed contact NC at a time 29seconds after the closing of the switch s1 of the control unit C. Thereset terminals generally designated R1A through R1D in the functionblock D12, the function block D10, the decade counter function block DCUand the decade counter function block DCT respectively cause a reset atzero time for the outputs each of these units to a digital one. Thismeans that a digital one must exist at the output terminal of theexclusive OR gate X01 to cause reset. If the control switch S1 is openedas it should be in this operative example a digital zero is placed onthe associated imput terminal of the exclusive OR gate X01. The ON delaywill provide a digital one at the P terminal of the exclusive OR gateX01. This will reset the previously described devices D12, D10, DCU andDCT as described. It will also place a digital one input on one terminaleach of the NOR gate N1 and the AND gate A1. Unless all of the inputterminals of the NOR gate N1 are zero, the output of the NOR gate N1will be zero. The output of the decade counters DCU and DCT will be zerounless the preset values 2 and 9 respectively have been attained inwhich case the outputs of the decade counters DCU and DCT will both goto one, where they will be respectively inverted by the inverters I5 andI6 and made digital zero. Since the two mentioned decade counters DCUand DCT have recently been reset, the outputs of the inverters I5 and I6will be one. Consequently, the output of the NOR gate N1 will be zero.As long as the output of the AND gate A1 is one, the output of the NORgate N3 will be zero. As long as this is the case, both input terminalsto the NOR gate N2 will be zero and its output terminals will be one andboth input terminals to the NOR gate N3 will be one and its output willbe zero. Such being the case, the associated input terminal of theexclusive OR gate X02 is zero and its control terminal or P terminal isone. Thus the output terminal of the exclusive OR gate X02 must be one.This provides a one to an associated input terminal of the AND gate A2and a one to one of the input terminals of the NOR gate N4. This causesthe output terminal of the NOR gate N4 to be zero which causes one ofthe input terminals of the NOR gate N7 to be zero. Since the output ofthe inverter I2 is zero, the associated input to the AND gate A3 iszero, and the output of the AND gate A3 must be zero. Consequently, theoutput of the NOR gate N7 must be one making the other input terminal ofthe NOR gate N4 one. When the synchronizing signal to the pulse train eterminal of the AND gate A2 is one the output of the AND gate A2 is alsoone thus causing the output of the NOR gate N6 to be zero consequentlylatching the NOR gates N5 and N6 in a manner similar to the way NORgates N4 and N7 were latched. When this happens, the output of theinverter I3 will be one and the output of the inverter I4 will be zero.If the output of the inverter I4 is zero, the thyristor th2 will be inan off state or non-conducting. If the output of the inverter I3 is one,the gate g1 of the thyristor th1 will be actuated causing the thyristorth1 to be turned on thus conducting current from the power supply PS1through the load LD1.

When control switch s1 is closed, a one is placed on the other input ofthe exclusive OR gate X01. This changes the output of the exclusive ORgate X01 to a binary zero thus placing a binary zero on one terminaleach of the NOR gate N1 and the AND gate A1 and on the reset line 82. Ifthere is a zero on one terminal of the AND gate A1, there is a zero onthe output terminal thereof, regardless of what happens at the otherterminal of the AND gate A1. This places a binary zero on one of theinput terminals of the NOR gate N3.

The train of pulses c1 propagates through the dividers D12 and/or D10 asthe case may be, through the range selector switch RS and into thecounters DCU and DCT until the preset time, in this case 29 seconds, haselapsed. After the elapsed time of 29 seconds, a digital one occurs atthe respective output terminal of each of the decade counters DCU andDCT. The digital ones are changed to digital zeros by the inverters I5and I6. Consequently, at this instant, all of the inputs to the NOR gateN1 are at binary or digital zero. This causes the output of the NOR gateN1 to go to one which causes the output of the NOR gate N2 to go to zerowhich thereby provides a zero on the other input terminal of the NORgate N3. Since the NOR gate N3 now has zeros on all its input terminals,the output of NOR gate N3 goes to one placing a one on the other inputterminal of the NOR gate N2. This latches the NOR gates N2 and N3.

The digital one on the output terminal of the NOR gate N3 is fed back tothe counter D12 where the set input terminal SE thereof is energized tofreeze or hold the count of the divide-by-6-portion D6 of the moduleD12.

The digital one on the input terminal of the exclusive OR gate X02 isinverted because of the presence of another digital one on the Pterminal of the exclusive OR gate X02. Consequently, the output terminalof the exclusive OR gate X02 is at a digital zero. Since this is thecase, the output of the inverter I2 goes to a digital one which places adigital one on one of the input terminals of the NOR gate N5 and on oneof the input terminals of the AND gate A3. The presence of the digitalone on the previously described input terminal of the NOR gate N5latches the NOR gates N5 and N6 into a disposition where a digital oneis on the output terminal of the NOR gate N6 and a digital zero is onthe output terminal of the NOR gate N5, and this is exclusive of thedisposition of the pulse train or enable terminal e of the AND gate A2.The digital zero on the output terminal of the NOR gate N6 is convertedto a digital one thus causing the output of the inverter I3 to go to adigital zero which in effect removes the gate drive from the thyristorth1 thus causing thyristor th1 to cease conducting which breaks thecurrent conducting path between the power supply PS1 and the load LD1.This action occurs almost instantaneously with the occurrence of thedigital one on the output terminal of the inverter I2. However, thedigital one on the input terminal of the AND gate A3 will not passthrough the AND gate A3 to change the status of the NOR gates N4 and N7until the proper enable signal is present on the e terminal of the ANDgate A3. This is true even though the zero from the output terminal ofthe exclusive OR gate XO2 has been quickly placed on one of the inputterminals of the NOR gate N4.

By referring now to FIG. 3, it can be seen that the previously describedpresence of digital zeros on every input terminal of the NOR gate N1,which led to the removal of gate drive from the thyristor th1, almostinstantaneously occurred when the clock pulse train c1 changed statefrom a digital zero to a digital one. It is to be recalled that thelatter action is necessary to index the elements D6, D10, RS, DCU andDCT. A positive going leading edge of the clock pulse c1 is shown inFIG. 3 at b. In order for the digital one to pass through the AND gateA3 in FIG. 2, a digital one must also be present on the pulse train orenable terminal e thereof. This pulse train or enable terminal e isconnected to the output of the divide by 2 portion D2 of the module D12at the line 78. The waveshape for this latter signal relative to thepreviously described clock signal c1 is indicated by pulse train e' inFIG. 3. It can be seen that as the clock signal c1 goes positive, the e'signal goes negative or to a digital zero and remains at that state forone cycle of the clock pulse c1. It is to be recalled that the output ofthe module D12 is no longer oscillating because of the action of the setsignal at the set terminal SE. However, the output of thedivide-by-2-module D2 is not set and it continues to oscillate such asis indicated at graph e' in FIG. 3. The digital one necessary to allowthe output of the AND gate A3 to go to a digital one will not occurrelative to the occurrence of the rising leading edge b on the clockpulse c1 until a time a as passed as shown in FIG. 3, in which case therise of the signal on line 78 will occur at d. Of course, once thishappens, the latch comprising the NOR gates N4 and N7 will change statebecause AND gate A3 has been enabled by the one on line 78.Consequently, a digital zero is placed on the output of the NOR gate N7which is converted to a digital one by the inverter I4 thus providinggate drive to the gate g2 of thyristor th2 which thus causes thethyristor th2 to turn on to conduct current and provide current flowthrough the power supply PS2 and the load LD2. The latter synchronizedaction between the solid-state contacts NC and NO provides a breakbefore make function for the output terminals NC and NO respectively ofthe relay device shown in FIG. 2.

Referring once again to FIG. 2, when it is desired to turn the thyristorth2 off, and the thyristor th1 on once again, or said in another way,when it is desired to once again open the normally opened contact NO andclose the normally closed contact NC the switch s1 is thrown the otherway to deenergize the control C. This will immediately provide a digitalone on the output terminal of the exclusive OR gate X01 which willimmediately reset all of the devices connected to line 82, namelydivider D6, divider D10, the decade counter units module DCU, and thedecade counter tens module DCT. At the same time, digital ones will beplaced on one input terminal each of the NOR gate N1 and the AND gateA1. The placement of the digital one of the NOR gate N1 will immediatelyswitch its output to zero, however the latch comprising the NOR gates N2and N3 will not switch states until the digital one provided to thepreviously described input terminal of the AND gate A1 is passed throughthe AND gate A1 by the occurrence of another digital one at the outputterminal of the NOR gate N8. There will not be a digital one on theoutput terminal of the NOR gate N8 until the clock bar signal c1 and theenable signal e on line 78 are both at zero. The coincident conditionoccurs when the clock bar pulse c1 and the enable pulse e shown in FIG.3 are at a disposition indicated by g and f. When this occurs, a zeroimmediately appears at the output terminal of the NOR gate N3 whichcauses the output terminal of the exclusive OR gate X02 to go to one.This puts a digital one on one of the input terminals of the AND gate A2and it also puts a digital one on one of the input terminals of the NORgate N4. The presence of the digital one on the NOR gate N4 immediatelycauses the output terminal of the NOR gate N7 to change to a digital onewithout any other event occurring, other than the latching of the NORgates N4 and N7. This then places a digital zero on the output of theinverter I4 which removes base drive current and voltage from the gateg2 of a thyristor th2 thus turning off the thyristor th2 at the nextcurrent zero of the power supply PS2 and consequently interrupting thecurrent flowing in the load LD2. However, the disposition of the digitalone on the previously described input terminal of the AND gate A2 willnot be passed through the AND gate A2 until the signal on the pulsetrain e terminal of the AND gate A2 is also at a digital one.

By examining FIG. 3 once again, and referring to the curves generallydesignated c1 and e' it can be seen that the pulse train e terminal willnot have a digital one signal thereon until incident d occurs, which isat least a time h after the thyristor Th2 is opened. Once the oneappears on the pulse train e terminal of the AND gate A2, the latchcomprising the NOR gates N5 and N6 will quickly change state to put azero on the output terminal of NOR gate N6 and a one on the outputterminal of the inverter I3. This turns on the thyristor th1 completingthe circuit between the power supply PS1 and the load LD1. It can beseen from the latter discussion that the break before make between thenormally opened contact NO and the normally closed contact NC occurswith respect to the opening of the switch s1 as well as with the closingof the switch s1.

The preceding illustrative example was directed to a case when there wasa desired ON delay after a specific period of time after the switch s1was thrown. It is to be understood with respect to the embodiments ofthis invention that OFF delay may also be accomplished in a similarmanner utilizing the apparatus shown in FIG. 2. In essence, thefunctions described with respect to the last mentioned illustrativeexample will be the same however, the order will be transposed.Consequently, it is not necessary to describe a function by functionoperation for accomplishing OFF delay. However, as an example, presumingit is desired to have an OFF delay after a period of 45 seconds, thecontrol element D would be disposed in the OFF delay mode, that is theoutput from the ON/OFF delay module D would be a binary zero. The switchs1 on the control element C would be disposed in the energized position,that is, a digital one would be present at the output terminal ofelement C. When this occurs, the normally closed contact NC will be openand the normally opened contact NO will be closed. This would beaccomplished with the synchronization and timing associated with thebreak before make function described previously with respect to thepreviously described operative illustrative example when the thyristorth1 was turned on and the thyristor th2 was turned off. The previouslydescribed synchronization between the presence of a change in outputsignal on the output terminal of the exclusive OR gate X02 and theenergization of the pulse train or enable terminals e of the AND gatesA2 and A3 would also be accomplished as was previously described. Whenthe switch s1 was opened, the control unit C would have a digital zeroat its output terminal and the previously described timing out functionwhich ultimately leads to a change in status at the output terminal ofthe exclusive OR gate X02 and the actions which follow would occur onceagain.

The various elements shown in FIG. 2 cooperate with the exclusive ORgate X03 and the light emitting diode means LED to give a three stateindication of the status of the normally opened and normally closedcontacts NO and NC respectively. During a time out state, the lightemitting diode LED flashes at a 10 hertz rate because of the 10 hertzsignal that is provided to one input of the exclusive OR gate X03 alongline 80 from the output of the divider D12 during timeout. Theillumination from the light emitting diode means LED may be 180° out ofphase with the signal on line 80 depending upon the status of the Pterminal of the exclusive or gate X03. If a one is on the P terminal asin an ON delay situation, the light emitting diode will be 180° out ofphase from its disposition during a situation when a zero is on the Pterminal as in OFF delay. In a preferred embodiment of the invention thelight emitting diode means LED may be dark before time out has begun,and may be illuminated after time out has been completed. In anotherembodiment of the invention, the light emitting diode means LED may beilluminated before time out begins and may be dark after time out hasbeen completed. In the preferred embodiment of the invention the lightemitting diodes means LED will be illuminated when a digital one existson the output terminal of the exclusive OR gate X03, and the lightemitting diode means LED will not be illuminated when a digital zero ison the output terminal of the exclusive OR gate X03.

It is to be understood with respect to the embodiments of thisinvention, that they may be adapted for use with integrated or discretecircuitry and with thick and/or thin film integrated circuit logicdevices. It is also to be understood with respect to the embodiments ofthis invention that the frequencies of the various signals are notlimiting but merely illustrative and that other frequencies may beutilized provided the synchronization between the input frequency andthe other frequencies is maintained.

It is also to be understood that devices Q1 and Q2 and devices th1 andth2 may be triacs, thyristors or silicone controlled rectifiers or anyother similar device which may be either isolated or non-isolated. It isalso to be understood that the photoresistive elements provide thedescribed break before make function by changing resistance more rapidlyin one direction than in the other.

The apparatus embodying the teachings of this invention have severaladvantages. One advantage lies in the fact that the apparatus is capableof providing a break before make function for its output contacts orcontrols. Another advantage lies in the fact that it provides amulti-state indication of the status of the output contacts.

What I claim as my invention is:
 1. A solid-state relay, comprising:a.control means for actuating solid-state contact means to change state;and b. a pair of complementary solid-state contact means interconnectedwith said control means one of which is generally opened and the otherof which is generally closed, said control means actuating each of saidsolid-state contact means to change state in which case said contactmeans which is closed will always open before said contact means whichis opened will close, each said solid-state contact means comprising alight emitting means interconnected with said control means whichproduces light in relationship to a signal from said control means, eachsaid contact means also comprising light sensitive resistance meansdisposed in light accepting relationship with said light emitting meansfor changing resistance between a higher and lower value of resistancein relationship to the change of light in the vicinity of saidresistance means, said light sensitive resistive means controlling thestate of said contact means, a predetermined amount of change of saidresistance causing said associated contact means to change state, saidchange of said resistance from said lower value of resistance to saidhigher value of resistance occurring at a different rate than saidchange of resistance from said higher value of resistance to said lowervalue of resistance consequently causing one said contact means to openbefore said other contact means closes.
 2. The combination as claimed inclaim 1 wherein said light emitting means comprises a light emittingdiode.
 3. The combination as claimed in claim 2 wherein said light fromsaid light emitting diode increases when said signal from said controlmeans is present.
 4. The combination as claimed in claim 1 wherein saidlight sensitive resistance means comprises a light sensitive resistor.5. The combination as claimed in claim 4 wherein said light sensitiveresistor decreases in resistance in relationship to said change of lightin the vicinity of said lighht sensitive resistance.
 6. The combinationas claimed in claim 5 wherein said solid-state contact means comprisethyristor means which cause said contact means to be open when saidassociated thyristor means is non-conducting and cause said contactmeans to be closed when said thyristor means is conducting.
 7. Thecombination as claimed in claim 6 wherein said decrease in resistancecauses said thyristor means to be non-conducting.
 8. The combination asclaimed in claim 1 wherein the changes of state of both said solid-statecontact means are delayed by an adjustable predetermined increment oftime after a signal is supplied to said control means for the purpose ofcausing said contact means to change state.
 9. The combination asclaimed in claim 1 wherein said control means comprises an integratedcircuit element.
 10. The combination as claimed in claim 1 wherein saidcontrol means comprises a thin film circuit element.